Electromagnetic Radiation Hazards on Humans Due to Mobile Phones

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1 Idia Jural f Sciece ad Techlg, Vl 9(0), DOI: /ijst/06/v9i0/85835, Ma 06 ISSN (Prit) : ISSN (Olie) : Electrmagetic Radiati Haards Humas Due t Mbile Phes A. Christia Jsephie Malathi Schl f Electrics ad Egieerig, VIT Uiversit, Near Katpadi Rad, Vellre , Tamil Nadu, Idia; achristia@vit.ac.i, achristiadmiic@gmail.cm Abstract There is a escalati i the amut f mbile phe users da b da with the availabilit f lw cst, highl featured mbiles i the maret. I the preset ivestigati, the radiati characteristics f cell phe had set is beig aaled at the frequec f 900 MH ad the iteracti f these radiatis with the huma bd is t be evaluated. The effects f radi frequec (RF) eerg are related t the rate f eerg absrpti ad it is cmputed usig the parameter specific absrpti rate. The specific absrpti rate (SAR) f EM radiati frm cell phes huma bd is beig aaled at the regis f si, muscle ad heart. A vel methd fr the mdelig f huma bd is carried ut usig the MATLAB sftware, which uses the fiite differece time dmai (FDTD) methd fr the SAR calculatis. Further its effects are beig aaled frm ur ivestigati ad it is reprted that the measured SAR are withi the FCC limits. Kewrds: EM (Electrmagetic Radiati), MOM (Methd f Mmets), RF (Radi Frequec), Radiati Haards, SAR (Specific Absrpti Rate). Itrducti There is a icreasig demad fr the use f wireless cmmuicati sstems alg with the ccer fr huma s ctact t EM radiati. This is mstl evidet i the usage f mbile phes. Ma cutries have set varius guidig priciples ad stadards fr limits fr expsure t RF radiati. EM Radiati ca be defied as waves f electric ad magetic eerg radiatig thrugh space. Cell phes ad its base statis prduce EM radiatis. These radiatis are bserved b their frequec ad pwer. The frequec rage fr the cell phe is arud 800 MH t 900 MH with a maximum pwer f watts. The pwer emitted is expressed i uits f milli watt per cm,. Whe huma bd is uprtected t EM radiati a iteral field is geerated i the bd. The absrpti f pwer b the tissues will cause a temperature rise which is depedet the clig mechaism f the tissue. The field prduced due t heatig depeds the frequec, tissue dielectric prperties ad surce cfigurati. Whe the therm regulatr capabilit f the sstem exceeds, tissue damage results. The Electrmagetic eerg absrbed per uit mass f tissue is called Specific Absrpti Rate (SAR) SAR = σe /ρ Where σ = Cductivit (m /m) ρ = Desit f the tissue (Kg/m 3 ) E = Iteral Electric Field (V/m) The SAR f EM radiati frm cell phes the huma bd is beig studied. A vel methd fr the mdelig f huma bd is beig carried ut b usig MATLAB sftware which empls the FDTD methd fr SAR calculatis. There are several techiques available fr measurig the full bd electrmagetic absrpti, but there is specific techique t calculate SAR withi the bd. MOM is a frequec dmai methd which was fllwed, still MOM requires strage memr f the rder f (3N) ad time fr cmputig f (3N) 3 where N is the umber f cells. The FDTD has bee used extesivel i cmputig the iteracti f EM fields with cmplex, lss dielectric bdies. This methd has memr ad time requiremets *Authr fr crrespdece

2 Electrmagetic Radiati Haards Humas Due t Mbile Phes prprtial t N. This Paper describes the FDTD methd ad utilit f the FDTD methd is demstrated b a 3D mdel f the huma bd mdel usig MATLAB sftware. The acquired results validate that the FDTD methd is capable f cmputig iteral field distributi with acceptable accurac.. Electrical Prperties f Bilgical Substaces The Electrical prperties f the bilgical substaces ca be classified as the active prperties ad passive prperties. Active defies the capabilit t geerate electrical ptetials ad fields while the passive describes the respses t exterall applied electrical stimuli. The absrpti f EM waves i full bd depeds frequec ad the psitiig f the electric field E t the dimesi L f the bd, where L is majr legth f the bd. The highest rate f eerg absrpti happes fr E ll L (E rietati) fr frequecies where majr legth is apprximatel 0.36 t 0.4 times the free space wavelegth (λ) f radiati. Uderstadig abut the electrical prperties is eeded t ivestigate the iteracti mechaism f EM fields. The huma brai creates electrical sigals ad alg with chemical reactis with which the bd parts cmmuicate. The huma brai weigh up t abut 3 puds ( gm) 3. The brai etails gra matter (40%), white matter (60%) ctaied iside the sull. The bld is a paque rather viscid fluid. Its specific gravit is abut.06 ad temperature is geerall abut 37 degree cetigrade. The heart is a bielectricall ctrlled bld pump. The heart f all mammals ctracts r beats i respse t a electric ptetial differece acrss it which reaches a maximum value just prir t the start f the bld pumpig ctracti. Electrical prperties are eeded t assess the rate f the eerg absrpti. The SAR is used t measure the effects f EM fields humas. The SAR is csidered sufficiet i mst cases t quatif the effects f the depsiti f thermal eerg i the bilgical sstems. There is a majr differece betwee the NRPB ad the IEEE specificall i the 0 t 000 MH rage as shw i Figure. ICNIRP figures are reduced half whe cmpared t the tw stadards abve GH. The Figure shws a cmparis fr the public categr. As per the stadards give b FCC, ANSI/IEEE ad NCRP, there is a limit EM absrpti i humas ad emissi frm RF devices give i terms f SAR. B FCC, RF absrpti limits are upt.6 watts/kg, ver e gram f tissue 4,5. 4. FDTD Methd The FDTD methd was prpsed b YEE ad the develped b Taflve. It is the sluti fr Maxwell s equatis 6,7. Figure e. Cmparis f ccupatial limits. 3. RF Expsure Limit Frequec ad itesit f the icidet EM field decides the expsure limit. The limits are set csiderig the average whle bd SAR t exceedig 0.4 wg - fr wrers ad 0.08 wg - fr geeral public, alg with experimetall determied threshld f 4wg -. Figure. Cmparis f public limits. Vl 9 (0) Ma 06 Idia Jural f Sciece ad Techlg

3 A. Christia Jsephie Malathi Apprximati f derivatives i discrete frm is de usig FD ad the time dmai simulatis idicate TD. I this methd, the regi csidered is divided it umber f cubic cells i which the fields are defied at fixed lcatis. Maxwell s equatis are discretied b usig the FD apprximati. After discretiig the Maxwell s equati, it is slved b prvidig the excitati field t the cells as a fucti f time, the iitial cditis ad the budar cditis. Extesivel used methd fr apprximatig EM. N matrices are ivlved i implemetig. Quic learig time. Wave iteracti ad cuplig mechaisms ca be studied. It is rbust, flexible, efficiet, versatile, user friedl t slve Maxwell s equatis i time dmai. It is widel used fr slvig pe regi scatterig, electrmagetic iterferece (EMI), Electrmagetic cmpatibilit (EMC). Advatages (a) It is simple. (b) N eed f itegral equatis, iversi f matrices. (c) Simple t implemet (d) Less memr requiremet. (e) Eas t cvert t frequec dmai frm time dmai. Disadvatages (a) Mdelig f surrudig is eeded alg with the bject mdelig. (b) Executi time is large. (c) Accurac is less whe cmpared t methd f mmets. (d) Cmputati cat be de fr curved surfaces. (e) The field quatities are w l at grid pits. Applicatis Atea/Radiati prblems Eigevalue prblems EM Absrpti i huma tissues 5. Elecrmagetic Simulati i Free Space The EM waves simulati geerated b a Pulse is studied. Maxwell s equatis i free space are give b E = t H e 0 () H = E t m 0 () Bth E ad H dete the electric field ad magetic field. Equatis () ad () ca be i expressed usig del peratr, = + + i j x Let E = (Ex, E, E). The crss prduct f ad E is give belw i j = E Ex E E Usig the abve expressis we rewrite () ad () as E H x t i j E H = = t e e E Hx H H H t H t H t H t x = m H H H E E i j = E E m Ex E E E E (3) (4) E field is i the directi f x plae ad waves travels i the directi (E = 0). E = H = 0, ad hece E = (E x, 0, 0). The E field ad H field travel at right agles t each ather ad hece E. H = 0. Sice E x 0 ad b er factr prpert H x = 0. As H = 0, we have H = (0, H, 0). Equatis (3) ad (4) chages t E H x t 0 = 0 e 0 0 (5) Vl 9 (0) Ma 06 Idia Jural f Sciece ad Techlg 3

4 Electrmagetic Radiati Haards Humas Due t Mbile Phes H t = Ex m 0 (6) Equatis (5) ad (6) idicates the wave prpagati i directi, as shw i (Figure 3) 6. The Algrithm Havig gt the sstem, we eed t apprximate E x ad H. crrespds t the chage alg the axis ad a time chage is deted b. B cetral differece apprximati i bth space ad time, we mdif (5) ad (6) as where + ( E ) x ( Ex) + ( H ) ( H ) ν = ε = e ( H ) ( H ) + ( Ex ) ( Ex ) + = m ad ν = µ The Figure 4 belw represets the FDTD grid created 8,9. The E x apprximatis are represeted b rage triagles while the H x apprximatis b vilet triagles. Each rw relates t a specific istat i time, at half time steps ad each clum idicates a e whle time step. The whle ad half steps are deted b the gra ad blue grid lie. The iitial values csidered are set as gree circles ad the brders are shw as rage ad vilet circles. FDTD Apprximati Grid Ever triagle has three arrws pitig twards it (Figure 4) 8,9. Of the three arrws, e arrw emerges frm Figure 4. the previus time step. The remaiig tw cmes frm a half-step dw ad a half-step t the right r left. It is clearl evidet that the algrithm is iter weaved i spatial ad time dmai similar t partial differetial equatis i time ad space. This techique is als amed as leap frg methd. Imagie a frg as triagle, fr istace ( E x ) E x + Figure 4 The FDTD Apprximati Grid. ad leapig his legs t jump up t the triagle, ( ). The path it maes first mves utward ad the iward maig a triagle ad the path draw b his legs mae a triagle. The magitudes f (5) ad (6) are t equal because f the permittivit f free space ad the permeabilit f free space, ε ad µ. Sice the values are mdified as, E = E= e E m m E e ad substitutig this i equatis (7) ad (8) we have + ( E ) ( H ) ( H ) ( E x = h x) ( H ) = h ( E x) ( E x) H + + ( ) + Figure 3. Waves. Prpagati f Trasverse Plae-Plaried EM where h = em 0 This methd is beig implemeted i ur prject b geeratig a icidet wave ad the equatis fr E ad H are slved. Huma bd mdel was created usig the dielectric prperties ad the cductivit. 4 Vl 9 (0) Ma 06 Idia Jural f Sciece ad Techlg

5 A. Christia Jsephie Malathi 7. Bd Mdel The calculated E ad H fields (Figure 5.) are categried it, The Ttal field The Scattered field The icidet wave is created alg e edge f the ttal field, prpagates thrugh the field ad is subtracted ut the ther ed. Hece, E ad H fields t reach the scattered field vlume are thse which are scattered ff the scatterer. This explais the implemetati f the radiati cditi. 8. Cstraits ad Limitatis The cstrait i this methd is the radiati cditi is t implicit ie. utgig scattered waves ma reflect bac it the scattered bject. This prblem ca hwever be vercme b itrducig a absrpti cditi arud the edge f each E field matrix which absrbs the utgig scattered waves. This is based a tw-ple expasi methd accrdig t Baliss ad Turel, which results i errr give b, Errr = O c p fr 5. (7) Where f - icidet frequec r - distace frm ceter f the scatterig bd t the budar f the cmputig field. Whe lw icidet frequec is used, large vlume surrudig the bd is eeded t vercme the errr due t imperfect trucati cditis. The stabilit ca be esured b taig the step sie as δt = δ/c (8) Ttal Field Scatterig Object Scatterig Fields Lattice Trucati Figure 5 5. A. Divisi f FDTD lattice it Ttal ad Scattered fields. Where δt - the time step δ - the cell sie c - speed f the electrmagetic waves The equati (8) idicates that the smaller step sie leads t mre umber f time steps (high resluti). 9. Results fr Huma Bd Mdel The Mdel fr the Huma bd is beig de b MATLAB sftware based FDTD methd. The results btaied are accurate, efficiet ad versatile. Here the SAR distributi is btaied usig icidet frequecies at 900 MH. The tabulati fr cductivit, relative permittivit ad mass desit f heart, muscle ad si at 900 MH frequec are shw i Table. The SAR distributi i huma mdel is shw belw i Figure Cclusi Fr cell phes peratig at 900 MH, the maximum value f electric field is calculated t be 400 V/m fr W pwer utput. But we have fud the Electric field stregths iside the bd with the icidet field f V/m. Irder t cmpare ur results accuratel, we d the fllwig calculatis. Assumig the cellphe is clidrical ad csiderig the atea legth l = λ (lambda), We w, C = f λ, λ = C / f, = (3 0 8 )/( ) = 0.33 m The Pwer desit at a distace r =.cm, frm the atea is rughl equal t p/πrl, sice earl all the radiated pwer has t pass thrugh a clider f area πrl. We w the pwer radiated b a cell phe at 900 MH is watts, ad hece p = watts. Substitutig the abve values Table. Tabulati fr cductivit, relative permittivit ad mass desit Tissue Name Frequec Cductivit (s/m) Relative Permittivit Mass Desit f the Tissue (Kg/m 3 ) Si 900MH Muscle 900 MH Heart 900 MH Vl 9 (0) Ma 06 Idia Jural f Sciece ad Techlg 5

6 Electrmagetic Radiati Haards Humas Due t Mbile Phes Figure 7. 6 cm Heart Field Figure Stregth 7 at 900 MH. Figure 6. Field Distributi at 900 MH - Si, Muscle, Heart i huma bd. At distace f 0 cm - Si At distace f 3 cm - Muscle At distace f 6 cm Heart the pwer desit is fud t be watts. Nw we have t fid the Electric field frm pwer desit. We w, E / R = pwer desit E = ( ) 0.5 = 9.59 V/m This will be the icidet field t the huma bd at 900 MH ad hece we ca multipl with the result which we btaied fr, with V/m. Thus the Electric field stregth btaied at differet tissue laers Si, Muscle, Heart are fud t be V/m, 8.8 V/m, 36 V/m ad are shw i Figure 6, 7. The btaied SAR f Si, Muscle, ad Heart are shw i Figure 8 ad tabulated belw i Table. These results are cmpared with the (Federal Cmmuicati Cmmissi) FCC limits fr geeral uctrlled/expsure (00 KH 6 GH) 0,. < 0.08 W/Kg Full Bd <.6 W/Kg Partial Bd The btaied Specific Absrpti rates are withi the FCC limits.. Future Develpmet EM radiati is all ver spread amg the evirmet. Because f the emergece f varius wireless services Figure 8. Table. Frequec (MH) Figure 8 Specific Absrpti Rate. Specific Absrpti Rate Si Muscle Heart W/Kg 0.36 W/Kg 0.75 W/Kg EM radiati is part ad parcel f the evirmet. The umber f mbile users has bee drasticall icreased. It was predicted t have. billi wireless device users arud the wrld b 005 ad.7 billi i 05. There is wa t ctrl this chage. EM radiati is als a id f plluti which shuld be ctrlled. Curretl all the researchers are wrig twards the prducti f harmless wireless devices. Smaller cell sie, imprved base stati ateas ad sme advaced techlgies will mae the cell phes t radiate less pwer. It is huge research tpic which eeds t be ivestigated further.. Refereces. Sadiu MNO. umerical Techiques i Electrmagetics. 009 April 9. 6 Vl 9 (0) Ma 06 Idia Jural f Sciece ad Techlg

7 A. Christia Jsephie Malathi. La Asma, Parhigar Naser. Effect f Presece f Huma Bd Atea Gai. Idia Jural f Sciece ad Techlg. 05 Nv; 8(30). Di:0.7485/ijst/05/ v8i/ Gadhi OMP. Bilgical Effects ad Medical Applicatis f Electrmagetic Eerg. 990 Ja ; p Sear SS, Demirbile BO, Mrgul A. SAR Assessmet i a huma head mdel expsed t radiati frm mbile phe usig FEM. IEEE Iteratial cferece Electrmagetic cmpatibilit, Mieaplis, Miesta. 00 Aug 9-3; : Berardi P, Cavagar M, Pisa S. Evaluati f the SAR distributi i the huma head fr cellular phes used i a partiall clsed evirmet. IEEE Trasactis Electrmagetic Cmpatabilit. 996 Aug 6; 38(3): Sulliva DM. Electrmagetic Simulati usig the FDTD Methd. 03 Ma Sulliva DM. The FDTD methd: cmputati ad Aalsis. 03; p Sulliva DM, Brup DT, Gadhi OMP. Use f Fiite Differece Time Dmai methd i calculatig EM absrpti i huma tissues. IEEE Tras. Bimed. Egg. 987 Feb; BME 34(): Sulliva DM, Gadhi OMP, Taflve A. Use f the Fiite Differece Time Dmai methd fr calculatig EM absrpti i ma mdels. IEEE Tras. Bimed. Egg. 988 Mar; 35(3): Fields E. Questis ad aswers abut bilgical effects ad ptetial haards f radifrequec electrmagetic fields. Federal Cmmuicati Cmmissi ffice f Egieerig ad Techlg. OET Bulleti 56, Furth editi. 999 Aug.. Mam A. Bilgical ptetial haards f electrmagetic fields the case f mbile phes. Cair, Egpt: Twetieth atial radi sciece cferece. 003 March Zamaia A, Hardima CY. Electrmagetic Radiati ad Huma Health: a review f surces ad effects. High Frequec Electrics. 005 Jul. Vl 9 (0) Ma 06 Idia Jural f Sciece ad Techlg 7